1. Field of the Invention
The field of the invention is that of measuring angles.
To be more precise, the invention concerns a sensor for determining the angular position of a cursor adapted to move and/or to be moved along a circular or more generally elliptical or even any shape closed path.
Sensors of this kind find applications in all types of devices and systems in which it is necessary to know the angular position of a member able to pivot about an axis.
2. Description of the Prior Art
Various more or less complex types of angular measuring device are already known. Thus there are contactless sensors based on inductive and/or capacitive electromagnetic circuits and electro-optical systems. These various devices are usually highly complex and often provide for only a small and finite number of distinct angle measurements.
Circular potentiometer sensors like that shown in FIG. 9 are also known. This known type device comprises two concentric tracks, a resistive outer track and a conductive inner track. A cursor rotating about the center of the two tracks short-circuits the tracks by means of two sliding contacts.
The resistive track is not continuous but has two ends between which a reference voltage may be applied. It will be understood that if a reference potential difference is applied between these two ends of the resistive track the voltage sensed at the conductive track is proportional to the angular position of the cursor.
This type of sensor therefore provides a simple way of measuring an angular position. It has a number of drawbacks, however, which restrict its use in many fields.
The major drawback of this device is that it requires a break in the circular resistive track to provide access to its ends so that the reference voltage can be applied. There is therefore a "dead" angle between these two ends within which it is not possible to measure the angle.
Mechanical abutments are usually provided to prevent the cursor from being positioned within this dead angle.
In this case displacement is limited physically, which makes it impossible to use the sensor in all cases in which the cursor is able to take up any angular position. Likewise, this sensor cannot be used if the cursor must be able to rotate more than once in each direction.
In some cases there are no mechanical abutments and the cursor can travel across the dead angle. In this case the sliding contact of the cursor leaves the resistive track between the start and the end of the dead angle. There is a break in the sliding motion which compromises the durability of the contact.
What is more, any position measurement carried out inside this dead angle yields a more or less random result which is not representative of the exact position of the cursor.
One objective of the invention is to palliate these various drawbacks of the prior art.
To be more precise an objective of the invention is to provide an angular position sensor enabling any angle between 0.degree. and 360.degree. to be measured continuously, the cursor being able to move over at least one complete revolution.
A specific objective of the invention is also to provide a sensor of this kind in which the position cursor can safely rotate through a plurality of turns in the same direction.
Another objective of the invention is to provide a sensor of this kind in which wear of the track and contacts is reduced and the durability of the sensor is increased.
Another objective of the invention is to provide a low cost sensor of this kind which is simple to manufacture and use industrially.
A further objective of the invention is to provide a method of determining the angular position measured by this sensor which is both simple and accurate.